Method of controlling seatbelt retracting device with motor

ABSTRACT

In controlling a seatbelt retracting device having a mechanism for retracting a seatbelt with a motor, a current flowing to the motor is detected, and a rate of increase in the current is calculated. When the rate of increase exceeds a predetermined value, the motor is stopped. When the current exceeds a predetermined value, the motor is stopped as well.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a method of controlling a seatbeltretracting device having a mechanism for retracting a seatbelt with amotor.

A seatbelt retracting device mounted to a motor vehicle or the like hasa function of winding an excess portion of a seatbelt after an occupantwithdraws the seat belt and attaches a tongue to a buckle device. Aconventional seatbelt retracting device is provided with a single returnspring for performing such a function. Accordingly, when an occupantwithdraws a seatbelt against an urging force of the return spring tofasten the seatbelt, and releases a hand after attaching the tongue tothe buckle, the seatbelt retracting device winds an excess portion ofthe seatbelt with a force of the return spring so that the seatbelt fitsthe occupant.

As described above, the seatbelt retracting device has the function ofwinding an excess portion of the seatbelt so that the seatbelt fits theoccupant. When the seatbelt is not used, the seatbelt retracting devicewinds the seatbelt until the seatbelt is completely stored in a storageunit. At the same time, when the seatbelt is used normally, the seatbeltretracting device needs to prevent an unnecessary pressure on theoccupant. However, in the seatbelt retracting device having the singlereturn spring, when an urging force of the spring is reduced toalleviate the pressure on the occupant, the urging force may not beenough to smoothly retract the seatbelt (for storing), thereby sufferingoperability and storability. In contrast, when the urging force isincreased to provide a sufficient retracting force for the retraction,an unpleasant pressure may be applied to the occupant.

Further, in the conventional seatbelt retracting device provided with asingle return spring, the return spring is wound as the seatbelt iswithdrawn, thereby increasing the urging force as the withdrawn amountof the seatbelt increases.

In order to solve the problems described above, there has been aseatbelt retracting device, in which a motor or a combination of a motorand a return spring winds a seatbelt, as disclosed in Japanese PatentPublication (Kokai) No. 2001-225720. Such a seatbelt retracting devicehaving a motor for retracting a seatbelt has been also disclosed inJapanese Patent Publications (Kokai) No. 11-301407 and No. 11-334533.

In general, a seatbelt retracting device with a motor is controlled toshut off power to the motor when a seatbelt is completely retracted. Ifthe power to the motor is left on when the seatbelt is completelyretracted, power source of a battery is wasted. Further, the motor maybe overheated, thereby making it necessary to use a motor with high heatresistance. Accordingly, in the conventional control system, a currentflowing to the motor is monitored. When the current exceeds apredetermined value, it is determined that the seatbelt is completelyretracted, and the power to the motor is shut off.

In the conventional control system, it is determined that the seatbeltis completely retracted when a relatively large current is detected, sothat it is possible to securely retract the seatbelt. However, in a casethat a part of an occupant, e.g. an arm, is caught in the seatbeltduring retraction, a retraction force of the motor tightens the part ofthe occupant, thereby imposing a pressure on the occupant. If theoccupant tries to withdraw the seatbelt during the retraction, it isnecessary to withdraw the seatbelt with a strong force against theretracting force of the motor.

The seatbelt retracting device may be deteriorated with time, and it isnecessary to increase a torque for winding the seatbelt, or an output ofthe motor is lowered. In such a case, if it is set to determine that theseatbelt is completely retracted at a relatively small current, it maybe determined that the seatbelt is completely retracted before theseatbelt is actually retracted completely, and the power to the motor isshut off, resulting in insufficient retraction.

In view of the problems described above, an object of the presentinvention is to provide a method of controlling a seatbelt retractingdevice with a motor in which it is possible to securely retract aseatbelt in a normal state. Further, it is possible to prevent apressure on an occupant when a part of the occupant is caught in theseatbelt, and to withdrawn the seatbelt with a small force duringretraction.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to a firstaspect of the invention, a method of controlling a seatbelt retractingdevice with a mechanism for retracting a seatbelt with a motor includesstopping the motor when a rate of increase in a current flowing to themotor exceeds a predetermined value.

In the first aspect of the present invention, the motor is stopped whenthe rate of increase in the current flowing to the motor exceeds thepredetermined value. In a normal case, when the seatbelt is completelyretracted, a load of the motor abruptly increases and the currentabruptly increases. The motor is stopped when the rate of increase inthe current exceeds a threshold, so that an excessive current does notflow to the motor after completion of the retraction. In a case that apart (for example, an arm) of the occupant is caught in the seatbelt,and the occupant withdraws the seatbelt during the retraction, thecurrent to the motor abruptly increases in an initial stage. As aresult, the rate of increase in the current exceeds the predeterminedthreshold, and the power to the motor is stopped. Accordingly, it ispossible to prevent pressure applied to the occupant and withdraw theseatbelt with a small force.

According to a second aspect of the present invention, in the firstaspect, the motor is stopped also when a current flowing to the motorexceeds a predetermined value.

In the first aspect, if the seatbelt retracting device by itself isdeteriorated and hence a large current is required for retraction, theremay be a case in which even when the current to the motor reaches asaturation value and retraction is almost completed, the rate ofincrease in the current to the motor is not large. In the second aspect,the motor is stopped also when the current flowing to the motor exceedsthe predetermined value. The predetermined value is set to a value closeto the saturation value of the current to the motor. Accordingly, it ispossible to stop the power to the motor upon completion of theretraction.

According to a third aspect of the present invention, in the first orthe second aspect, the motor is not controlled for a predeterminedperiod from a moment when the motor is activated.

Immediately after the motor is activated, a counter electromotive forceof the motor is small, so that an accelerated current flows and thecurrent flowing to the motor abruptly increases. In the first and thesecond aspects, the rate of the current or the current may exceed thethreshold and the motor may stop. In the third aspect, the motor is notcontrolled for the predetermined period from the moment when the motoris activated. Accordingly, it is possible to prevent malfunction due tothe accelerated current immediately after the motor is activated.

As described above, according to the present invention, it is possibleto provide the method of controlling the seatbelt retracting device witha motor in which the seatbelt is securely retracted in the normal state.Further, even when a part of the occupant is caught in the seatbelt, itis possible to withdraw the seatbelt with a small force during theretraction without imposing a pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a structure of a device to which acontrolling method is applied according to an embodiment of the presentinvention;

FIGS. 2( a) and 2(b) are charts showing a current and a rate of increasein the current with time for explaining a controlling method of Mode 1,wherein FIG. 2( a) shows a normal state, and FIG. 2( b) shows a statethat a part of an occupant is caught in a seatbelt;

FIGS. 3( a) and 3(b) are charts showing a current and a rate of increasein the current with time for explaining a controlling method of Mode 2,wherein FIG. 3( a) shows a state that a torque required for retractingthe seatbelt is increased, and FIG. 3( b) shows a state that a torquerequired for retracting the seatbelt is further increased; and

FIG. 4 is a chart showing a current and a rate of increase in thecurrent with time for explaining a controlling method of Mode 3.

DETAILED DESCRIPTION OR PREFERRED EMBODIMENTS

Hereunder, embodiments of the present invention will be described withreference to the accompanying drawings. FIG. 1 is a schematic diagramshowing a structure of a device to which a method of controlling isapplied according to an embodiment of the present invention. In FIG. 1,reference numeral 1 designates a seatbelt retractor (main body of aseatbelt retracting device), reference numeral 2 designates a springmechanism, reference numeral 3 designates a clutch, reference numeral 4designates a reduction gear, reference numeral 5 designates a motor,reference numeral 6 designates a motor control circuit, and referencenumeral 7 designates a current detecting circuit.

The seatbelt retractor 1 is connected to the spring mechanism 2, and tothe reduction gear 4 via the clutch 3. The reduction gear 4 is directlyconnected to the motor 5. The motor control circuit 6 turns on and offpower supplied to the motor 5 and the clutch 3.

When an instruction to drive the seatbelt retractor by the motor 5 isissued to the motor control circuit 6 via an external signal (notshown), the motor control circuit 6 turns on the power to the motor 5and the clutch 3, so that the seatbelt retractor 1 engages the reductiongear 4.

The current detecting circuit 7 detects a current flowing to the motor5, and sends a detection signal to the motor control circuit 6. Themotor control circuit 6 reads a current value detected by the currentdetecting circuit 7 at a predetermined time interval, and calculates adifference with respect to a value read previously. The power suppliedto the motor 5 is stopped according to a mode selected from three modesdescribed below.

Mode 1

The power distribution to the motor 5 is stopped when the difference ora differential value of the current exceeds a predetermined threshold.

Mode 2

The power distribution to the motor 5 is stopped when the difference orthe differential value of the current exceeds the predeterminedthreshold, or when the current value exceeds a predetermined threshold(different from the threshold of the difference or the differentialvalue).

Mode 3

Control in Mode 1 or Mode 2 is not executed after a predetermined periodof time when the power is supplied to the motor 5.

An operation in these control modes will be described in detail below.FIGS. 2( a) and 2(b) are charts showing an operation of the motorcontrol circuit 6 in Mode 1. FIG. 2( a) shows a state that the seatbeltis retracted in a normal way, and FIG. 2( b) shows a state that a part(for example, an arm) of an occupant is caught in the seatbelt duringthe retraction. Solid lines represent an actual current value and anactual rate of increase in the current, and hidden lines represent acurrent value and a rate of increase in the current when the power isnot stopped.

When the power distribution to the motor 5 is started, the current valueabruptly increases initially. Then, the seatbelt is retracted and thecurrent value increases gradually as the load increases. When theseatbelt is completely retracted and not retracted any more, the motor 5stops and the current increases abruptly. The motor control circuit 6obtains the rate of increase in the current by differentiating an outputof the current detecting circuit 7 or calculating a difference withrespect to a previous measured value. The motor control circuit 6 stopsthe power distribution to the motor 5 when the rate of increase in thecurrent exceeds the predetermined threshold. In this manner, the powerdistribution to the motor 5 can be stopped when the seatbelt iscompletely retracted.

As shown in FIG. 2( b), the load of the motor 5 increases when a part(for example, an arm) of the occupant is caught in the seatbelt duringthe retraction. As a result, the current value abruptly increases andthe rate of increase in the current exceeds the threshold. Accordingly,the motor control circuit 6 stops the power distribution to the motor 5.Therefore, the power distribution is stopped at the moment when themotor 5 still generates a small retracting force, thereby preventingpressure applied to the occupant.

FIGS. 3( a) and 3(b) are charts showing an operation of the motorcontrol circuit 6 when the seatbelt retractor 1 is deteriorated and thetorque required for retracting the seatbelt is increased, or when themotor 5 is deteriorated and an output torque is lowered.

FIG. 3( a) shows a state that the torque required for retracting theseatbelt is increased. Solid lines represent the case that the torquerequired for retracting the seatbelt is increased, and thin hidden linesrepresent the initial state as shown in FIG. 2( a). Thick hidden linesrepresent the current value and the rate of increase in the current whenthe power is not stopped. In such a case, the current value required forretracting the seatbelt increases, and the rate of increase in thecurrent also increases. However, the motor control circuit 6 detects therate of increase in the current and stops the power distribution to themotor when the detected value exceeds the threshold. Accordingly, thepower distribution to the motor is stopped at the moment when theseatbelt is completely retracted as shown in FIG. 3( a).

In contrast, in a conventional device, the power distribution to themotor is stopped when the current value reaches the predeterminedthreshold. Accordingly, depending on the threshold, the powerdistribution to the motor may be stopped before the seatbelt iscompletely retracted when the torque required for retracting theseatbelt increases.

FIG. 3( b) shows a state that the torque required for retracting theseatbelt is further increased. Solid lines represent the case that thetorque required for retracting the seatbelt is further increased, andthin hidden line represents the initial state as sown in FIG. 2( a).Thick hidden line represents the current value and the rate of increasein the current when the power distribution is not stopped. In this case,when the seatbelt is completely retracted, the current value almostreaches the saturation value, and the rate of increase in the currentdoes not increase even when the retraction is completed.

Accordingly, in the method shown in FIGS. 2( a) and 2(b) or FIG. 3( a),there is a case in which the power distribution may not be stopped. Insuch a case, the control method in Mode 2 is used, in which the powerdistribution to the motor 5 is stopped when the current value exceedsthe predetermined threshold and the rate of increase in the currentexceeds the predetermined threshold. The threshold of the current valueis preferably slightly smaller than the saturation value of the current.In other words, Mode 2 is preferably applied to a secondary control inwhich the power distribution to the motor 5 is stopped in a state thatthe rate of increase in the current does not increase because thecurrent value is saturated.

FIG. 4 is a chart for explaining the control in Mode 3. There may be acase that a large accelerated current is generated depending on thespecification of the motor 5 when the motor 5 is turned on, so that therate of increase in the current exceeds the predetermined threshold setin Mode 1 in an initial acceleration state shown in FIG. 4. In such acase, the power distribution to the motor 5 is stopped, thereby stoppingthe normal retracting operation. Therefore, in Mode 3, the control ofthe motor 5 is not executed during the initial driving stage of themotor 5, i.e. for a predetermined period (preferably slightly longerthan the period until the acceleration is completed) from the momentwhen the power distribution to the motor 5 is started.

In Mode 1, the motor is driven only in the range indicated by the solidline shown in FIG. 4. In Mode 3, the power distribution to the motor 5is stopped when the retraction proceeds and is completed as usual asshown by the hidden line, or a part of the occupant is caught in theseatbelt.

The disclosure of Japanese Patent Application No. 2003-322854 has beenincorporated in the application.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

1. A method of controlling a seatbelt retracting device with a motor,comprising: supplying electricity to a motor for retracting a seatbelt,detecting the electricity flowing to the motor for retracting theseatbelt at a predetermined interval, calculating a difference withrespect to a value read previously to find a rate of increase in theelectricity, awaiting a predetermined period since the electricity issupplied to the motor, and starting to control the motor includingstopping the motor when the rate of increase of the electricity exceedsa predetermined rate.
 2. A method of controlling a seatbelt retractingdevice according to claim 1, wherein said stopping the motor is alsomade when the electricity flowing to the motor exceeds a predeterminedvalue.
 3. A method of controlling a seatbelt retracting device accordingto claim 1, wherein said electricity is current.
 4. A method ofcontrolling a seatbelt retracting device according to claim 1, whereinsaid motor is connected to the seat belt through a clutch, said motorand clutch being controlled by a control circuit.
 5. A method ofcontrolling a seatbelt retracting device according to claim 1, whereinsaid predetermined time since the electricity is supplied to the motoris a substantial period until an acceleration of the motor is completed.